Incorporation of polar functionality, including epoxy functionality, onto nonpolar base polymers has been the subject of many recent patents and publications. These functional group containing polymers have many utilities, such as impact modifiers for engineering thermoplastics, and elastomers with increased service temperatures. Epoxy modified polymers may be prepared by grafting epoxy containing monomers to base polymers by either solution processes or by melt processes.
Shiraki et al., in U.S. Pat. No. 4,657,971, disclose the use of functionalized block copolymers of styrene and butadiene as impact modifiers for polar engineering thermoplastics and a process to prepare these functionalized polymers by melt phase grafting functional monomers to base block copolymers. Acceptable functional groups include epoxy groups.
Oliver, in published application WO 86/04076, discloses an epoxy modified EPDM rubber which is useful as an impact modifiers for polyesters and a process to prepare the epoxy modified EPDM rubber. Oliver's rubber is functionalized by solution grafting an ester of an alpha-beta unsaturated acid which has an epoxy functionality on the alkoxy portion of the ester. Examples utilize glycidyl acrylate and glycidyl methacrylate as the ester.
Solution grafting of functional monomers to polymers is advantageous over melt grafting because the base polymer is less degraded by the grafting process. But solution grafting is often uneconomic because of the extended holding times required for the reaction to take place. Solution reaction generally requires reaction times of from one half to two hours. Dissolving the polymers and subsequent recovery of the solvent are also necessary and add to the expense of the process. Melt phase grafting is therefore the preferred grafting method when the resultant degradation of the polymer can be tolerated.
Melt phase grafting of epoxy containing monomers can also result in the epoxy rings being opened by hydrolysis of the epoxy to two hydroxyl groups. Melt phase grafting of glycidyl acrylate at conditions typical of extrusion grafting maleic anhydride (about 260.degree. C.) results in about 80 percent of the epoxy rings on the grafted monomers being hydrolyzed. The resultant hydroxyl functional groups are not as effective as epoxy groups because they are generally not as "reactive" or as polar as the initial epoxy groups. To result in a desired level of epoxy functionality, melt phase grafting requires the grafting of additional functional monomers due to the grafted functional monomers which have been converted to hydroxyl functionality. Grafting the additional functional monomers is generally undesirable because it causes exponentially increasing degradation of the base polymer.
It would be desirable to have a melt phase grafting process to graft epoxy functional groups to base polymers in which a large amount of the epoxy rings are not opened by the grafting process. It is therefore an object of the present invention to provide a process to melt phase graft epoxy containing monomers to the base polymers wherein the grafted monomers retain a high level of epoxy functionality. In the preferred embodiment, it is a further object to provide a process to melt graft epoxy functionality to the base polymers in which the base polymers are not excessively degraded by the melt grafting process.